SHOULD DYNAMIC SCRUTINEERING BE CHANGED? ARE OTHER TESTS NEEDED TO CHECK STABILITY?
In ASC2003, the dynamic scrutineering consisted of a figure-8 test and a braking test.
Was this testing adequate? Too challenging? Not challenging enough?
What are your thoughts? How to submit your response.
RESPONSES (Generally listed with newest response first.)
RESPONSE#9
Well, speaking from our survey of the '03 race route, your
car would be in pieces in fairly short order [refers to Response#7] - the roads are pretty darn
bumpy. Also, from a safety perspective, you probably don't want the car
so low to the ground than an SUV could easily run over the top of you...
FROM: Robert Vogt
RESPONSE#8
I feel to lower the cars would be a bad approach. If anything there
should be a min. road clearance. Stability is not a problem for a well
designed chassis so we should be working on design and NEVER remove
safety factors.
FROM: Malcolm Stalcup
RESPONSE#7
Hi all !
Here's a thought. Why was the rule added to have the drivers eye level at
70cm ? I'm going to assume to keep the cars at the same height as other
road traffic for crash impact reasons.
I brought this up because, with these cars so high off the ground (CG wise)
there must be alot of weight transfer in cornering. Of course this is what
causes alot of stability problems. That said, would lowering the cars be possible ?.. or has this issue been
looked at before ? Personally, I'd have the belly pan no more then 3-4" off
the ground.
FROM: Colin Fitzgerald
RESPONSE#6
I don't know if rollover really is much of a concern considering how short
most of our solar cars are. Skidding, sliding, and spinning are much
greater problems. The cars are MUCH more likely to do the latter than the
former since the CG of the cars is normally only a little more than a
foot or so off the ground. It would take the car sliding sideways into a
curb at high speed to flip most of them, and even then, I suspect the
suspension of most cars would be sheared off before the car even started
to flip. There just isn't enough lateral traction in the Michelins or
Bridgestones to worry about. The only way to really look at dynamic
stability is to run a practical test, ideally some type of obstruction
avoidance test like a slalom or something similar.
FROM: Jason Kramb,
University of Michigan Solar Car Team Alumni,
Driver / Chief Aerodynamics and Body Design Engineer '99,'01
RESPONSE#5
To speak to 3 wheelers and rolling over calcs, let me say first that I
agree with Rolla guys who spoke to this earlier. If you design and build
your CG into your car correctly, it can be a very stable design as was
proven in ASC 03 when Minnesota, my team, got a flat tire in the back
wheel on a loose gravel road. The car did not veer to the right or left,
it stayed going straight ahead the whole time, with minor instability.
To calculate rollover, you can calculate the hard turning/cornering g-force
which it takes to flip your car. Minnesota found that it takes
approximately ballpark the same amount of cornering g's to tip the car as
it does to make an ngm tire slip/slide laterally, based on theoretical spec
numbers for friction coefficients. This simple calculation based upon
track, wheel base, and cg location vertically and horizontally are probably
from the same basic equations used in whatever standard Steve Hayslett
speaks of. As for providing measured numbers, this would involve driving
your car like a bat out of hell if you designed it correctly. Theoretical
values is the furthest extent that any cornering data should have to go.
FROM: Jason Halpern,
University of Minnesota - Twin Cities,
Mechanical Engineering,
Team Manager,
Solar Vehicle Project
RESPONSE#4
I agree using performance-based regulations rather than prescriptive
regulations would be much better. This leaves things open to creativity
while getting closer to the intent of the regulation.
As an example, the Ontario Highway Traffic Act specifies that bicycles
must have a rear brake capable of stopping the bike in X feet, and X
amount of reflective tape on the front forks. My trike
(tricolour.net/gtvs6.html) does not have a rear brake at all, and really
doesn't need it, since it has dual front disk brakes that easily exceed
the performance intent of that law. Also, there are no front forks on
my trike.
slainte mhath,
FROM: Richard Guy Briggs
RESPONSE#3
NHTSA uses a calculation called Static Stability Factor (SSF) to estimate a
vehicles propensity for rollover. If a vehicle has a SSF lower than 1.2 it
is pretty much assured to roll in a situation where drastic steering inputs
are used. Many SUV's like the Bronco II which are famous for rollovers, have
a SSF around .9. Only a few SUV's currently have a SSF over 1.2. Most cars
have a SSF greater than 1.2.
Perhaps having teams provide theoretical and practical measurement of the
SSF is something ASC could implement. SSF is only an indication of rollover
risk, losing control of the vehicle and skidding off the road is a whole
other issue.
Regards,
FROM: Steve Hayslett,
Project Engineer,
New Generation Motors
RESPONSE#2
Another excellent idea [refers to Response#1]. I would rather see a car's stability really
tested rather than limit design ideas. I would think that this test
would need to be such that it could be set up in the same area that the
current braking test is done in. As Dan has pointed out to me, space is
often limited where ever we are having scruitineering and such tests
need to be able to tell the inspectors as much as possible about the car
in as little space as possible.
FROM: Jason Kramb,
University of Michigan Solar Car Team Alumni,
Driver / Chief Aerodynamics and Body Engineer '99,'01
RESPONSE#1
[Note: This was originally written for the wheel configuration question.]
I've seen four wheel vehicles that had questionable stability and three
wheels vehicles that where very stable. Instead of dictating the number of
wheels to get an certain stability, The race should instead dictate a
certain stability and allow teams flexibility in achieving it. Wheel base,
trac, and CG should all be carefully considered in designing a vehicle.
When the original dynamic tests regulations for Sunrayce were drafted over a
decade ago, they probably didn't have a 520 lb solar car going 65 mph in
mind. Now this performance has been achieved, while the dynamic stability
regulations have changed little, if any. Dynamic tests during qualifying
should be updated to reflect the wheights and speeds of today's solar cars.
I propose the addition of a new High Speed Dynamic Regulation. A good test
of this regulation would be weaving 5 cones (TBD spacing) at a TBD speed,
say 40 mph. Because of the higher speeds, this test would occur after a
vehicle has passed all current dynamic tests. Failure to pass this test
would not result in failing to qualify, but would result in a lower speed
cap (say 50 mph) during the race. This makes it in the best interest of
every team to design a more stable car, especially if they plan on going
fast.
FROM: Nathan Rues,
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